That depends if it's a gallon of melted ice cream, or solid ice cream in a gallon sized tub. [ Here is an answer from answer.yahoo: A gallon of ice cream weighs about 5 pounds and contains 4 quarts.
One scoop of ice cream is 12 cup or about 68 grams.
One gallon contains 16 cups, so one half-gallon contains 8 cups ]